Method for the production of a shaft-hub connection

ABSTRACT

A toothed or splined shaft having an external toothing is pushed with clearance into an internal toothing of a hub, tooth to space, and the external toothing of the shaft is pressed together with the internal toothing of the hub. In the push-in position of the shaft, the latter is deformed plastically out of a cavity of the shaft in a radial circumferential widening operation and, so as to provide freedom from clearance between the spaces of the external toothing of the shaft and the internal toothing of the hub, the internal toothing engaging into the external toothing is pressed against the hub in such a way that the hub is deformed elastically and a press fit between the shaft and the hub is produced.

BACKGROND AND SUMMARY OF THE INVENTION

This invention relates to a method for making a shaft/hub connection.

A generic method is known from German publication DE 43 02 726 A1. Inthis case, in a first step to make the assembled connection, the hub andthe shaft are designed in such a way that the internal toothing of thehub and the external toothing of the shaft are coordinated with oneanother in terms of their dimensions, so that, when the shaft is pushedinto the hub, a clearance fit is obtained between the two hub/shaftassembled parts. However, before the shaft is pushed into the hub, theinternal toothing of the wheel hub is upset on an end-face portion, sothat the tooth spaces of the internal toothing on this portion have asmaller width in relation to the remaining part of the hub. The shaft isthen slipped into the hub portion having the original space width and issubsequently pressed through the hub portion provided with the smallerspace width. In this case, the internal toothing of the portion havingthe smaller space width and also the external toothing are subjected tovery high mechanical stress, with the result that damage to thetoothings when the shaft is being pressed through may occur, this being,in particular, against the background of the inclusion of themanufacturing tolerances of the individual parts (shaft, hub). In orderto keep the tolerances within narrow limits and thus counteract the riskof the damage referred to, a very high outlay in terms of themanufacture of the individual parts is necessary. Furthermore, theabovementioned upsetting, on the one hand, is an additional work step,thus increasing the cycle time during the making of the connection, and,on the other hand, can be reproduced only with difficulty and requireshighly accurate and therefore complicated process management. Moreover,the problem of axial tolerances of the shaft has a major bearing, since,after the shaft has been pressed through the hub, positioning on thelatter to achieve the desired exact relative position of the shaft inrelation to the hub is virtually impossible to correct.

One object on which the invention is based is to develop a genericmethod to the effect that it becomes possible in a simple reproducibleway to make a shaft/hub connection which optimally satisfies therequirements of dynamic loads.

This object is achieved according to the invention.

By virtue of the invention, the shaft can always be pushed into theexact axial assembly position in a simple way, since, in this first stepfor making the assembled connection, there is full play between theshaft and hub and no jamming or even pressing occurs when the shaft isbeing pushed through. As an accompaniment, any damage to the toothingswhich is associated with this is also avoided. Narrow manufacturingtolerances of the toothings of the shaft and hub and of their axial andcircumferential dimensions no longer play any part in the reliability ofthe production process, so that, on the one hand, cost-effectivematerials, even without any heat treatment, and simple productionmethods can be used for the hub and the shaft and, on the other hand,the particularly considerable outlay in terms of apparatus and time forfulfilling required narrow manufacturing tolerances in the assembledconnection may be dispensed with. Thus, overall, the reproducibility ofthe assembled connection is fully ensured. Furthermore, by a hollowshaft being used specifically for the method, there is a weight savingin the assembled connection and therefore material resources areutilized more effectively. As a result of the circumferential pressureagainst the hub due to the widening of the hollow shaft, highnon-positive and positive locking between shaft and hub is achieved,which is fully compatible with the dynamic loads. That is to say, no fitclearance occurs during the dynamic load, and there is also no increasein the clearance, and therefore direct torque transmission, without anytime delay, is ensured. The fit clearance is prevented by thenon-positive component of the connection on account of the elasticreformation of the hub. In addition, as a result of this non-positive orfrictional component, a high resistance force against axial displacementof the hub on the shaft after assembly is generated. Moreover, a highlong-term durability of the assembled connection is achieved, since thetoothing is not shaken during the operating time. The disturbingrattling noises associated with fit clearance when the teeth knockagainst one another also do not arise. Process management duringassembly is also simplified, the shaft/hub connection requiring only twowork steps, to be precise the pushing of the shaft into the hub and thewidening of the shaft.

Expedient refinements of the invention may be gathered from certainclaims; moreover, the invention is explained in more detail below bymeans of an exemplary embodiment illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a shaft/hub connection according to theinvention,

FIG. 2 shows, in cross section, the connection from FIG. 1 in thepush-in position of the shaft,

FIG. 3 shows an enlarged detail of the connection from FIG. 2,

FIG. 4 shows, in cross section, the connection from FIG. 1 after thewidening of the shaft,

FIG. 5 shows an enlarged cross section of the connection from FIG. 4,and

FIG. 6 shows a modified shaft construction.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a shaft/hub connection 1, in which an end portion 3of a hollow shaft 4, the end portion being provided with an externaltoothing 2, projects through a hub 5. The hollow shaft 4 may be designedas a toothed shaft or, as here in the exemplary embodiment, as a splinedshaft. The splined shaft can be produced in a simple way, for example,by drawing a tube or by milling that portion 3 of the hollow shaft 4which is intended for the formation of the toothing. The correspondinginternal toothing 6 of the hub 5 can be generated by reaming or else bymilling. Referring to FIG. 6, is also conceivable for the hollow shaft 4to be formed from two separate structural parts, a toothed rim 4 a and asmooth-cylindrical tube 4 b, the toothed rim 4 a which forms theexternal toothing 2 of the hollow shaft 4 being pushed onto the tubeinto the desired axial assembly position and subsequently being fastenedunreleasably to the tube, for example, by welding or by a partialwidening of the tube brought about by means of a fluidic internal highpressure applied in the tube. The teeth 7 and the spaces 8 of theexternal toothing 2 of the hollow shaft 4 of a conventional tubematerial have a prismatic design. The internal toothing 6 of the hub 5is configured correspondingly. The splined shaft 4 is then pushed withclearance, with its external toothing 2, into the internal toothing 6 ofthe hub 5, tooth to space, an assembly gap 9 being formed between thetoothings 2 and 6 (FIG. 2 and, in particular, FIG. 3).

After the exact axial relative position between the hollow shaft 4 andthe hub 5 is reached, what may be referred to as a widening lance ispushed into the inner space 10, forming the cavity, of the hollow shaft4. An axial duct for carrying a fluidic medium which is under highpressure runs in the widening lance, the duct possessing a radial borewhich is positioned at the location of the widening to be produced. Theradial bore is sealed off, resistant to high pressure (>approximately500 bar), in both axial directions by means of two radial seals arrangedon the circumference of the widening lance on both sides of the boreoutlet. That is to say, only that location of the hollow shaft 4 whichlies between the two radial seals is acted upon by the internal highpressure, and, therefore, the hollow shaft 4 is partially deformed. Bythe fluid high pressure being controlled, the sequence of the wideningprocess and the pressure force and therefore the strength of thefrictional lock can be set in a highly accurate way, as required,though, of course, within the framework of the breaking elongation ofthe hollow-shaft material and the deformation elasticity of the hub 5.

The hollow shaft 4 is thus circumferentially widened plastically in theradial direction, until the external toothing 2 comes into firmcircumferential bearing contact against the internal toothing 6 of thehub 5, with the fit clearance still existing up until then beingcancelled (FIGS. 4 and 5). When the frictional and positive locking ofthe hollow shaft 4 and hub 5 is achieved as a result, there remains atmost only a radial gap 11 between the toothed tips 12 of the teeth 7 ofthe external toothing 2 of the hollow shaft 4 and the respective facingspace bottom 13 of the spaces of the internal toothing 6 of the hub 5,as may be seen particularly in FIG. 5. The hub 5, admittedly, alsowidens momentarily, but only in the elastic range, so that, after thepressure is relieved, the hub material springs back elastically towardsthe plastically widened hollow shaft 4, thus affording particularly highfrictional locking between the shaft 4 and the hub 5.

There are, locally, several possibilities for widening. On the one hand,widening, and correspondingly, pressing may take place locally only atparticular points, for which purpose the hollow shaft 4 having theexternal toothing 2 is pressed continuously onto the internal toothing 6of the hub 5 at at least one axial position within the extent of thehub, thus making production, particularly in the case of a wideningmethod, applied to the hollow shaft 4, particularly rapid.

On the other hand, the shaft 4 may be widened in its axial extentlocally and selectively at the location of the hub 5 along the entireaxial overlap region of the toothings 2 and 6. In this case, thenon-slip hold of the hub 5 on the hollow shaft 4 is advantageous interms of the fatigue strength of the hold, since the torques acting onthe shaft/hub connection can be distributed broadly over the overlapregion. Moreover, even relatively high torques can be transmittedwithout damage.

Furthermore, it is conceivable for the hub 5 and the shaft 4 to beassembled in the push-in position in a closed internal high-pressureforming die. In this case, not only that portion 14 of the hollow shaft4 which lies in the overlap region of the toothings 2 and 6 at thelocation of the press fit to be made can be widened, but also theportions 15 lying outside the overlap region. The hollow shaft 4 may inthis case be widened over its entire extent. This results, for the hub5, in an axially positive embedding into the hollow shaft 4 and,consequently, in an immovable axial hold. If the widening is restrictedonly to the overlap region, a shaft/hub connection or a production ofthe assembly which saves construction space, as compared with thelast-mentioned variant, can be achieved. A closed internal high-pressureforming die is not necessary for this purpose, so that the use of theabovementioned widening lance is sufficient.

After the desired shaft/hub connection is made, in the case of action byinternal high pressure the latter is relieved and the widening lance isdrawn out of the hollow shaft 4. By the regulation of the internal highpressure being capable of being controlled in a highly accurate manner,the widening operation can be coordinated exactly with the respectivewall thickness of the hollow shaft 4 and/or with the breaking elongationof the hollow-shaft material in a careful and advantageous way by meansof a single die, so that process reliability is further improved.

Alternatively to widening by means of fluidic internal high pressure,this may also be carried out by drifting or reaming. The shaft/hubconnection according to the invention may be used, for example, ingearwheel, chain and belt mechanisms in the drive train of motorvehicles.

1. A method for making a shaft/hub connection comprising: providing atoothed or splined shaft having external prismatic teeth and a hubhaving internal teeth and prismatic spaces between the internal teeth,pushing the external teeth with clearance into the spaces, tooth tospace, plastically deforming the shaft in a push-in position of theshaft by way of a cavity of the shaft in a radial circumferentialwidening operation and elastically deforming the hub, withoutplastically deforming the hub, so as to produce firm circumferentialbearing contact between lateral faces of the external teeth and theinternal teeth and so that the external teeth engaging into the spacesproduce frictional and positive locking between the shaft and the hub,and maintaining a radial gap between tips of the external teeth andrespective surfaces, facing the tips, of the spaces.
 2. The methodaccording to claim 1, wherein the shaft is widened in an axial extentlocally and selectively at a location of the hub.
 3. The methodaccording to claim 1, wherein the shaft is widened over its entireextent.
 4. The method according to claim 1, wherein the shaft is widenedby means of fluidic internal high pressure.
 5. The method according toclaim 1, wherein the shaft is hollow and is manufactured from a toothedrim and a smooth-cylindrical tube which define two separate structuralparts, and wherein the toothed rim forms the external teeth and ispushed onto the tube in the correct position and then fastened bywelding or by a widening of the tube brought about by a fluidic internalhigh pressure applied in the tube at the location of the toothed rim. 6.The method according to claim 2, wherein the shaft is widened by meansof fluidic internal high pressure.
 7. The method according to claim 3,wherein the shaft is widened by means of fluidic internal high pressure.8. The method according to claim 2, wherein the shaft is hollow and ismanufactured from a toothed rim and a smooth-cylindrical tube whichdefine two separate instrumental parts, and wherein the toothed rimforms the external teeth and is pushed onto the tube in the correctposition and then fastened by welding or by a widening of the tubebrought about by a fluidic internal high pressure applied in the tube atthe location of the toothed rim.
 9. The method according to claim 3,wherein the shaft is hollow and is manufactured from a toothed rim and asmooth-cylindrical tube which define two separate instrumental parts,and wherein the toothed rim forms the external teeth and is pushed ontothe tube in the correct position and then fastened by welding or by awidening of the tube brought about by a fluidic internal high pressureapplied in the tube at the location of the toothed rim.
 10. The methodaccording to claim 4, wherein the shaft is hollow and is manufacturedfrom a toothed rim and a smooth-cylindrical tube which define twoseparate instrumental parts, and wherein the toothed rim forms theexternal teeth and is pushed onto the tube in the correct position andthen fastened by welding or by a widening of the tube brought about by afluidic internal high pressure applied in the tube at the location ofthe toothed rim.
 11. The method according to claim 6, wherein the shaftis hollow and is manufactured from a toothed rim and asmooth-cylindrical tube which define two separate instrumental parts,and wherein the toothed rim forms the external teeth and is pushed ontothe tube in the correct position and then fastened by welding or by awidening of the tube brought about by a fluidic internal high pressureapplied in the tube at the location of the toothed rim.
 12. The methodaccording to claim 7, wherein the shaft is hollow and is manufacturedfrom a toothed rim and a smooth-cylindrical tube which define twoseparate instrumental parts, and wherein the toothed rim forms theexternal teeth and is pushed onto the tube in the correct position andthen fastened by welding or by a widening of the tube brought about by afluidic internal high pressure applied in the tube at the location ofthe toothed rim.